This invention relates to the field of laser surgery, and more particularly to improved laser surgical methods and apparatus for increasing or stimulating revascularization or angiogenesis of myocardial heart tissue and thus the flow of blood to heart muscle.
Using various surgical techniques, some of which have been widely taught, medical science has developed several procedures for counteracting the effects of cardiovascular disease including open heart and bypass surgery.
More recently, another alternative form of cardiovascular surgery has been developed which is known as Transmyocardial Revascularization (TMR). Generally, in this TMR procedure, the surgeon accesses the patient""s heart by either percutaneous means or by an open incision, then proceeds to utilize a laser apparatus for creating a plurality of channels in the myocardial muscle tissue that forms a wall of a major heart chamber such as the left ventricle. Clinical tests have shown that the creation of a plurality of channels serves to increase flow of blood to the myocardial muscle tissue so as to establish a new vasculature that enables the heart to absorb more oxygen and be revitalized. Various forms of TMR procedures are disclosed in prior art United States patents such as U.S. Pat. No. 4,658,817 (Hardy), U.S. Pat. No. 5,125,926 (Rudko, et al) and U.S. Pat. No. 5,380,316 (Aita, et al) and also, more recently in co-pending application Ser. No. 08/607,782 which is assigned to the assignee of this invention. All of the aforesaid patents and applications disclose a procedure which utilizes laser energy that ablates the myocardial tissue at spaced apart locations to consume it in order to form a plurality of channels in the wall of the ventricular chamber of the patient""s heart. As blood flows into each channel formed, a revascularization process takes place which supplies additional oxygen to the heart muscle tissue and thereby revitalizes it. Although the beneficial effects of creating such channels in the wall of the patient""s heart chamber have been established, certain risks involved with such procedures have also been recognized. For example, if too many channels are formed during one procedure, there is a risk that a certain patient""s heart will react negatively to the trauma of the procedure or become weakened by it in some manner.
The present invention solves the aforesaid problem by providing a method and apparatus that enables the surgeon to stimulate the myocardium to cause revascularization rather than ablate the tissue at several locations to create channels. Thus, for some patients, the stimulation procedure creates a revascularization effect which strengthens the heart""s myocardial muscle tissue without negative effects thereto.
It is therefore one object of the invention to provide an improved method and apparatus for causing transmyocardial revascularization by stimulating the myocardium with less laser power, by creating temporary channels with diameters sized so the channels will close with time, and by creating spaced apart stimulation zones within the myocardium.
The present invention covers a method and apparatus for Transmyocardial Revascularization (TMR) procedures which provides for stimulating the myocardium of the heart muscle rather than creating open channels in it as in prior TMR procedures. Within the context of the present invention, the term xe2x80x9cstimulatingxe2x80x9d or xe2x80x9cstimulusxe2x80x9d means a TMR procedure wherein channels, zones or pockets of lased tissue are formed in the myocardium which are not open, or do not remain open, to the ventricular chamber of the heart. Revascularization or angiogenesis of the lased channels, zones or pockets occurs by means of introduction of blood born growth and healing factors and stimulated capillary growth surrounding the lased zones or pockets to create an increased supply of oxygen to the tissue and thus a revitalization of the heart muscle.
Revascularization or angiogenesis of the lased channels and/or zones will occur in the following ways: First, blood born growth and healing factors can be introduced to the site of stimulus (injury) as blood follows a lased or mechanical channel created by a laser fiber. The source of new blood and growth factors may be from the ventricle or from the surrounding myocardium. This combination of laser induced injury and blood born healing factors will act together to trigger revascularization. Secondly, the human myocardium displays elements of certain direct blood pathways similar to those found in reptilian hearts. In the present invention these pre-existing pathways can be inter-connected by using stimulus and lasing pockets in the myocardium. The overall effect is to increase the opportunities for capillary beds to become interconnected. Development of collateral coronary vessels is well documented in coronary literature. This can be viewed as an enhanced means for promoting new vessel growth. Lastly, the coronary muscle may be previously injured, thereby creating angina pain for the patient due to the net balance of blood flow and conditions left by a prior heart injury. By stimulating the heart, a new set of injuries (stimulus) is created which triggers a new healing response; in effect, re-injuring the myocardium in a controlled manner and re-initiating the healing process. The healing response is accompanied by increased blood flow from one of the first two methods outlined. The healing with stimulus occurs with or without the long term patent or open channels and blood supply via a continuous TMR channel from the ventricle.
In one embodiment of the invention, an optical fiber having a tapered distal tip is forced through the epicardium of the ventricular wall and into the myocardium. Once into the myocardium tissue, laser energy is emitted from the distal tip of the optical fiber radially outwardly at an angle from the longitudinal axis of the fiber element.
In another embodiment, a device with multiple, narrow optical fibers is used to create a relatively dense pattern of stimulation channels. In a third modification, the epicardium may be pierced with a tapered needle for introduction therethrough of a flat ended fiber. Additionally, access through the epicardium may be made through a single hole and a laser fiber tip may be angled in different directions to create several stimulation sites.
During a typical TMR stimulus procedure according to the invention the distal tip of an optical fiber element is moved axially in increments to various depths within the myocardium. At each incremental depth, the distal tip may also be rotated as a laser pulse is emitted radially outwardly from the axis of the optical fiber. Depending on the configuration of the distal tip the laser energy may be projected in a plurality of different directions from the fiber axis. During this procedure, the laser energy is at a relatively low level that limits its travel distance within and the amount of ablation of the myocardial tissue. Each beam or burst of laser energy from the distal tip of the fiber creates a partially ablated pocket or zone wherein angiogenesis can occur due to capillary action within the pocket. Thus, for each penetration of the fiber element within the myocardium a pattern of stimulus pockets or zones are created in the tissue surrounding the fiber element. Alternatively, stimulation may be created by alternating high and low power pulses to predisposed channels that do not remain patent. In a typical TMR stimulus procedure a plurality of stimulus penetrations (e.g. 20-40) in the heart wall are made at spaced apart locations and each penetration may produce 10-20 temporary channels, pockets or zones at various depths and at different locations around the optical fiber axis. Yet, in accordance with the invention the distal tip of the optical fiber need not penetrate through the endocardium into the ventricular chamber, although such penetration is not excluded.
A device according to the invention, for controlling the penetration depth and direction of the laser energy comprises a hand-held instrument controlled by the surgeon. Within a body portion of the device a shuttle grips the fiber element to facilitate its forward and backward movement in increments. Using the device the surgeon can advance the fiber element incrementally within the myocardium as laser bursts are triggered at intervals to create stimulus zones. The full axial travel of the fiber element can be preset to limit such travel to an amount less than the thickness of the myocardium. In accordance with the invention the hand-held instrument may control the axial movement of a fiber element by mechanical or electrical means.
Other objects, advantages and features of the invention will become apparent from the following detailed description of embodiments, presented in conjunction with the accompanying drawing.